Since I started working in renewables 15 years ago, there was always an assumption that burning wood was the greenest option available. However an increasing focus on air quality over the last few years has shown that this is unfortunately not the case...
There is always more than one way to look at an issue, and here we have to consider that there are 2 main impacts to burning wood - one is CO2 emissions and the other is pollution: specifically PM2.5s will be discussed here. PM2.5s are small particles of matter with a diameter of 2.5 micrometres (µm) or less. They are linked to increased incidences of cardiopulmonary and respiratory diseases, especially in urban areas. In the UK, mortality figures are estimated by different sources to be in the 30-40,000 range.
Firstly lets take CO2 emissions. Burning wood is green right? I mean Low carbon? Yes it is, if you are talking about burning locally sourced logs or chips that have not travelled that far from where they were cut. But many people are astonished to find out that burning wood pellets is actually worse in carbon terms than burning oil in an oil boiler. How is this true when burning wood is always described as Carbon Neutral? It comes down to the fact that processing and compressing the wood into pellets and then transporting what is essentially not a very energy dense fuel, has quite a significant cost. It is also not strictly accurate to say the burning wood is carbon neutral - it is true that burning will only release whatever CO2 was absorbed during the trees life. But releasing all of that CO2 in one fell swoop when the tree is burnt is in fact not that helpful when we are trying to limit CO2 emissions. In fact if you were to leave the trees standing and burnt natural gas instead, it would lead to lower emissions.
In terms of pollution, burning wood is bad news, full stop. Here's some headline facts from you, with sources.
More than half of Europe's sooty pollution is caused by domestic wood burning, around 2.5 times more than all vehicles - Clean Heat Background paper
Few people who install wood stoves are likely to understand that a single log-burning stove permitted in smokeless zones emits more PM2.5 per year than 1,000 petrol cars and has estimated health costs in urban areas of thousands of pounds per year - http://woodsmoke.3sc.net/health
'Biomass boilers are an expensive way to make climate change worse and reverse over a century of public health improvements’ - David Olivier as quoted in "Biomass - a burning issue".
In short - if you are going to burn wood then please make sure it is done as efficiently as possible. Make sure your flue is gas tight, the seals around the doors are good and that you burn the wood as hot as possible, to ensure the most thorough combustion. Evidence shows that when you burn wood, the PM2.5 and other pollution often sinks from the chimney, and is then drawn back into the house due to the negative pressure created by the wood burner. At the end of the day you are poisoning yourself! And of course adding to a very significant problem we have in the UK at the moment.
If you are wondering what the solution is to truly low carbon heating (other than putting on a jumper or two) - the answer is a well installed heat pump - whether that is air, water or ground source. They all perform significantly better in CO2 terms than any other technology and are also very low output in pollution terms too.
More info in future blog posts...